Method of preparing butadiene



Patented .Zune 15, 1943 METHOD OF PREPARING BUTADIENE Per K. Frolich, Westileld, and Byron M. Vanderbilt, Oranford, N. J., assigno'rs, by mesne assign ments, to Jasco. Incorporated, a corporation of Louisiana No Drawing. Application December 30, 1939, Serial No. 311,836

1 Claim.

This invention relates to the production of butadiene and more particularly it relates to improvements in the production of butadiene from 2-butene.

Butadiene is a very desirable raw material as an intermediate for the preparation of numerous chemical derivatives and for the production of synthetic rubbers, some of which are in many ways superior to natural rubber with respect to abrasion resistance, resistance to oxidation, etc. The uses of such synthetic rubbers have been restricted due to the high cost of manufacture when compared to the cost of manufacture of various articles when natural rubber is used. The high cost of the production of such synthetic rubbers is largely due to the involved processes so far developed for the preparation of butadiene. The best known process is the one in which acetylene is first, formed and then hydrated to form acetaldehyde, which is in turn condensed to aldol and then hydrogenated to butylene glycol and finally dehydrated to butadiene. Evenif good yields are obtained in the individual reactions, considerable losses are incurred in the handling and the processes are too extensive to make possible the preparation of cheap butadiene. The processes in which butadiene is formed directly from other hydrocarbons have heretofore been commercially impractical due to the small yields that are obtained per pass.

It has long been known that thermal cracking of aliphatic hydrocarbons results in the formation of some butadiene in practically all cases. Where parafiln hydrocarbons are cracked, the

yield of butadiene varies from a fraction of 1% Ill to about 3%. Yields of butadiene from the pyrolysis of mono-olefins had been reported to be higher than those from the corresponding saturated hydrocarbons but in no case has the yield of butadiene been sufficient to justify the commercial production of this diolefln by the cracking of an aliphatic hydrocarbon. I

In experiments carried out previously, 2-butene has been cracked at atmospheric pressures to obtain very low yields of butadiene. Wheeler and Wood, in the Journal of the Chemical Society of 1939, page 1819, report that it is possible to crack 2-butene in a temperature range of 600 to 900 C. and at a contact time of from to seconds to obtain 0.4 to 1.7% of butadiene. Practically identical products were obtained when cracking either l-butene or 2-butene under these conditions. Tropsch, Parrish and Eglofi, in the Industrial and Engineering Chemistry, vol. 28, page 581, of 1936, state that fairly good yields of butadiene from 2-butene may be obtained when operating at a highly reduced pressure. A pressure of 50 mm. of mercury and a temperature of 1100 C. are cited as being highly favorable operating conditions in order to get maximum yields of butadiene. However, cracking operations unby column 1.

der a vacuum of this order are difllcult and expensive to carry out. These difliculties and the high reaction temperature make such a process totally unsuitable for large scale production of butadiene.

It is an object of this invention to provide improvements in the cracking of 2-butene to obtain larger yields and a simple and more emcient method of producing butadiene.

According to this invention, it hasbeen found. that by maintaining proper temperature and contact time relationships, yields of butadiene from cracking 2-butene at atmospheric pressures can be obtained which are not only much greater than those previously obtained at atmospheric pressure but are also greater than those previously reported at reduced pressures. Contact times of less than 0.5 second and preferably less than 0.02 second in a maximum 30 C. range of the cracking zone are essential. The temperature of the cracking is regulated so as to get the desired conversion and this in general lies within the range of 775 to 925 C. It has also been found that it is highlyadvantageous to cool the cracking gases very quickly to at least 500 C. after they leave the cracking zone. This shock or quick cooling of the cracked gases serves two purposes: First, it brings the temperature of the gases quickly below the pyrolytic temperatures after they pass through a maximum in order to keep secondary reactions to a minimum. Secondly, it reduces the temperature of the butadiene to temperatures at which polymerization reactions are a minimum.

2-butene begins to decompose at'a fairly rapid rate at temperatures above about 650 C. However, as stated above, better yields of butadiene are obtained when the cracking temperature is much higher than this. Thus it is advantageous to raise the temperature of the butene rapidly to the maximum cracking temperature employed and then to cool it rapidly to a non-pyrolytic and'non-polymerizing temperature as soon as the desired conversion has occurred. The following Table I illustrates how the yield of butadiene from the pyrolysis of 2-butene may be increased for a given conversion by operating at relatively high temperatures and short contact times:

Table I Contact Percent conversion i time i ture, C. mamas yleldl 828 0.01 420 791 0.015 4412 c 0.14 3&0 838 0.015 3 7 0.14 mg 672 4.5 mg

1 Based on the amount otz-butene reacted, i. 0., converted as shown Although butadiene decomposes at a higher temperature than does Z-butene, it is very unstable at elevated temperatures due to its tendency to polymerize to ,higher molecular weight compounds. This tendency increases with temperature and concentration. The following data illustrate the behavior of various mixtures of butadiene in nitrogen at elevated temperatures:

gen enhance the loss of the butadiene. In any case it was found that it is highly desirable to cool the cracked gases containing butadiene as quickly as possible after they leave the cracking zone. This may be accomplished by shock cooling of the cracked gases by several known methods. A water cooler may be placed immediately.

after the heating zone with short, but adequate, insulation separating the two. The gases may be passed directly into a stream or spray or cold water or oil. Cool gases may be mixed with the exit gases immediately after leaving the heating zone. For economical reasons, it is preferred to use an external water cooler or water spray in order to cool the cracked gases. Butadiene is separated and the unreacted butene may be recycled.

The gas containing 2-butene may be prepared by means of various methods, that is, gas oil may be cracked and the products fractionated to obtain a fraction consisting substantially of hydrocarbons containing 4 carbon atoms to the molecule, the gas treated with 55-65% sulfuric acid at 20 C. to remove isobutylene and is then contacted with sulfuric acid of about 80-90% concentration at to C. wherein the normal butenes are dissolved. The sulfuric acid extract is diluted to 60-65% sulfuric acid and is then steam stripped and the normal butenes are recovered as a gas consisting of about 94% 2-butene and 6% l-butene. Another method of preparing 2-butene is to dissolve 2-butanol in sulfuric acid of 50-65% concentration, followed by heating the acid to a temperature of about 70 to 90 C. and

recovering 2-butene as an overhead. Other methods of preparing and segregating 2-butene may be likewiseused, such as catalytically dehydrogenating normal butane to l-butene and 2-butene, which in turn may be absorbed in 80-90% sulfuric acid and regenerated as predominately 2-butene. Small amounts up to about 6% of l-butene are generally found to be presented in theseparated gas containing 2-butene. Even after the 2-butene has been reacted to form butadiene and the butadiene separated. the ratio proportions of 2-butene and l-butene in the separated fraction of unreacted hydrocarbon which may be recycled is substantially the same as that in the initial charge. It is well blown that at elevated temperatures either l-butene or Z-butene isomerizes to an equilibrium mixture of the two oleflns. If when cracking either 2-butene or l-butene the rise in temperature is relatively slow, isomerization becomes complete prior to the cracking reaction and the same products are obtained when contacting either. However, by this new and improved process, isomerization is avoided and as shown by Table III yields of butadiene and other cracked products vary greatly when cracking the two isomers. Table III also shows that it is highly advantageous to employ normal butenes which are predominately 2-butene.

2-butene was cracked at 827 to 829 C. (maximum temperature) at a flow rate of 24 cc./sec. through a i. d. quartz tube in which was placed an it" quartz tube which was closed at one end. Contact time was the order of 0.1 sec.

in the temperature range of 800 to 829 C. The exit gas was passed through a trap cooled by ice and water and then caught in a 5-gallon carboy over saturated salt solution which had previously been saturated with some of this same gas. A portion of the gas was liquefied and rectified in a Podbielniak column in the regular manner. C1 was then run for hydrogen and methane obtained by diflerence. C2 and C: were united and total unsaturates obtained. C4 was run for butadiene and total unsaturation. Previous analyses had shown isobutylene to be absent. Acetylene analysis was run on a portion of the original exit as.

A total of 13.630 cc. of 2-butene were introduced into the furnace and 17,650 cc. were obtained along with 0.5 cc. of liquid product. The conversion of Z-butene was 42.3% and 35.6 moles of butadiene were formed for each 100 moles of butene reacted.

The following table shows comparative yields when cracking Z-butene and l-butene respectively:

Table III Percent Percent Constituent in cracked gas g i ss,

Z-butene i-butene H: 5. 5 2. 4 CH4 l5. 6 l2. 8 CIHA. 5. 6 l0. 2 OsHu ll. 7 l2 0 CIHI. I. 1 l. 4 C Hu ll. 8 7. 6 n-C4H|. 45. 2 45. 6 iso-Cdi; 0. 0 0. 8 ll-CaHm. 1.4 2.0 2.4 5. 2 Percent conversion 41. 5 46. 9 Percent yield (043.) 36.3 19.0

At the same conversion, e. g. 46.9%, one would expect a 34.8% yield of butadiene from Z-butene as compared to 19% obtained in the case of lbutene.

PER K. moucn. BYRON M. VANDERBILT. 

